Prospective, randomized, double-blind, multicenter, placebo controlled study to compare the safety and efficacy of repeated topical application of 1% penciclovir cream with placebo for the treatment of recurrent herpes labialis. Eligible patients will be assigned to either penciclovir or placebo and will initiate treatment within one hour of the first sign or symptom of herpes labialis. They will be assessed for symptoms and signs within 24 hrs of treatment initiation, then daily until loss of crusts, then alternate day until skin is "normal".